You forgot to go into you're devices files and export the file, to do that click where it says for example [you're Roblox account name].zip click on it and hold the files and then it will pop it up as export, and then you will get the textures and do what this guy is doing in the rest of the video.
Hi, im here to help: If you get ur character turned gray, simply just import all the photos of you avatar texture to your 3D (Avatar texture is come png, and automatically downloaded when you download ur character)
The editing app is (AVU editor) www.google.com/url?sa=t&source=web&rct=j&url=play.google.com/store/apps/details%3Fid%3Dcom.iMMcque.moshow%26hl%3Den_GB%26gl%3DUS%26referrer%3DDgoogle%2526Dorganic%2526Davu%2Beditor%26pcampaignid%3DAPPU_1_pvWEY6DcNomPgQbn5JugBQ&ved=2ahUKEwigx-fquNH7AhWJR8AKHWfyBlQQ5IQBegQIBxAF&usg=AOvVaw2Wr5-menhjjaiaH4329wbB